The use of a transducer (or "transmitter", as it is sometimes referred to) to measure the pressure of a fluid in a pipe is well known and established in the processing industry. Typically, the transducer has an impedance which is a function of the pressure being sensed. Hence, the current flowing through the transducer is a measure of the pressure sensed. In order to insure that the current is an accurate measure of pressure, there is a need to calibrate the transducer frequently.
The transducer is normally hardwired between the production line and the power source. A disadvantage associated with hardwiring the transducer is that, upon transducer failure, the production line must be shut down so that the failed transducer can be replaced with a new one which must be hardwired into the production line. The necessity of hardwiring a replacement transducer contributes to costly downtime of the production line.
Further, the in-line testing of the transducer is time-consuming. In order to calibrate the transducer, a cover must be removed and the power leads must be disconnected from the transducer and connected to the calibrating instrument. Additionally, removal of the cover from the transducer unnecessarily exposes the terminals and elements therein to caustic or corrosive atmospheres.